Image data to be registered is classified into two types; one is the raster type consisting of density data of each pixel; the other is the vector type consisting of vector data following the contour of a configuration. A compacting method is also proposed. The run length method is one compacting method. These types of data are selected according to the usage of the data. A new type of data is proposed by the invention of the present invention using Freeman's chain code.
For inputting image data, an image scanner is usually used. The image scanner generates raster data and has problems of long input time because of immense amounts of data. It takes a long time to process data outputted from an image scanner.